The invention relates to a new process for the resolution of DL-Mandelic acid. More particularly, it relates to a process for the resolution of DL-Mandelic acid in a two-phase liquid medium by the use of novel optically active 2-benzylamino-1-butanols.
The novel optically active 2-benzylamino-1-butanols which are useful in this process are represented by Formula (I), ##STR3## wherein X represents chloro, bromo, fluoro, nitro or methyl. A related pending application, to a process for the resolution of DL-mandelic acid, is U.S. Application Ser. No. 18,695 filed Mar. 8, 1979 which is a continuation application of U.S. application Ser. No. 831,025 filed Sept. 6, 1977 now abandoned.
The use of optically active amines such as quinine, (-)-.alpha.-(1-naphtyl)ethylamine, (+)-2-amino-1-butanol, (-)-menthylamine, and the like, to resolve racemic mixtures of carboxylic acids, such as tartaric acid, mandelic acid, aspartic acid, and the like, is well known in the art.
Applicants are not aware of any prior art reference which, in their respective judgements as one skilled in the art of resolving DL-Mandelic acid, would anticipate or render obvious the novel process of the instant invention; however, for the purpose of fully developing the background of the invention and establishing the state of the requisite art, the following references are set forth: Germ. Offen. 2,007,177 which discloses the formation of an optically active ammonium salt by reaction of the dextro- or levo-rotatory 2-(benzylamino)-1-propanol and cleavage of the said ammonium salt with dilute hydrochloric acid to recover the optically active acid. An English language abstract of this reference is contained in Chem. Abs. 73, 120417 (1970). U.S. Pat. No. 3,553,257 which discloses the preparation of dextrorotatory 2-amino-1-butanol. Beilstein 4, 291 which discloses the preparation of levo-rotatory 2-amino-1-butanol.
Since none of the known optically active amines has been found to be completely satisfactory, research continues in order to find new compounds and processes which will be more satisfactory. The present invention arose out of such research and resulted in surprising discovery that racemic mixtures of mandelic acid can be readily resolved in a two-phase liquid mixture of water and a water-immiscible organic solvent with the compounds of formula (I). The process of this invention is useful for the resolution of racemic mixtures of mandelic acid. The utility of D-(-)-mandelic acid and its derivatives, or L-(+)-mandelic acid is known in the art. See, eg., Germ. Offen. 2,415,402 and Germ. Offen. 2,436,686, an English language abstract of which is disclosed in Chem. Abs. 82, 31343m (1975) and Chem. Abs. 83, 10556 p (1975), respectively.